1. Field of the Invention
The present invention relates to a control apparatus for controlling a radiotherapy irradiation system employing X rays and proton beams, which are delivered to a tumor in a human body.
2. Description of the Related Art
FIG. 11 shows functional blocks of an arithmetic unit included in a conventional control apparatus for controlling a radiotherapy irradiation system proposed by Bortfeld et al. in 1990 (Physics in Medicine and Biology, 1990, Vol. 35, No. 10, pp.1423-1434), thus describing arithmetic operations performed by the arithmetic unit. There are shown an initial solution calculating means 101, a restrictions input means 102, an evaluation function setting means 103, an iterative calculation means based on a quasi-Newton's method 104, and an optimal solution output means 105. These operations are carried out according to a program by means of the arithmetic unit included in the control apparatus for controlling the irradiation system.
FIG. 12 shows the configuration of the above sort of control apparatus for controlling an irradiation system. Shown in FIG. 12 are an arithmetic unit 1, a display unit 2, and an input unit 3. The arithmetic unit 1 performs a series of operations according to a program (not shown). The display unit 2 is realized with a display device or the like. The input unit is realized with a keyboard or mouse. Incidentally, the irradiation system R is an object to which the results of the arithmetic operations are output.
An initial solution is calculated using a projection and reconstruction method devised for the modality of X-ray computed tomography (CT) (101). Thereafter, restrictions are input according to a prescription written out by a radiation oncologist (102). An evaluation function is set under the restrictions (103). Iterative calculation is performed according to a quasi-Newton's method, and an irradiated beam weight is determined for optimizing irradiation (104). An optimal solution indicating the optimal irradiated beam weight is output to the irradiation system R. Consequently, irradiation is carried out optimally. As far as a control apparatus for controlling an irradiation system in reality is concerned, a radiation oncologist observes a distribution of absorbed doses in a human body which is displayed on the display unit 2. The distribution of absorbed doses is obtained through arithmetic operations performed based on the calculated conditions for irradiation. The radiation oncologist then judges whether or not to adopt the conditions for irradiation. If the distribution of absorbed doses in the human body is unsatisfactory, the prescription is modified in order to set new restrictions. An optimal solution indicating an optimal beam weight is calculated under the new restrictions. As the evaluation function, for example, formula (1) is adopted.                                                                         F                ⁡                                  (                  x                  )                                            =                            ⁢                                                                    r                    0                                    ⁢                                                                                                          A                        ⁡                                                  (                                                      Dx                            -                                                          p                              1                                                                                )                                                                                                            2                                                  +                                                      r                    0                                    ⁢                                                                                                          B                        ⁡                                                  (                                                      Dx                            -                                                          p                              2                                                                                )                                                                                                            2                                                  +                                                                                                      ⁢                                                                    ∑                                          i                      =                      1                                        n                                    ⁢                                                            r                      i                                        ⁢                                                                                                                    R                          ⁡                                                      (                                                          Dx                              -                              u                                                        )                                                                                                                      2                                                                      +                                                      ∑                                          i                      =                      1                                        n                                    ⁢                                                            r                      i                                        ⁢                                                                                                                    S                          ⁡                                                      (                                                          Dx                              -                              c                                                        )                                                                                                                      2                                                                                                                              (        1        )            
Now, the first term of the formula (1) expresses a restriction on a minimum dose in a tumor, and the second term thereof expresses a restriction on a maximum dose in the tumor. The third term of the formula (1) expresses a maximum dose in a normal tissue, and the fourth term thereof expresses a restriction on a maximum permitted volume fraction of a normal organ at risk to receive more than a predetermined dose. A coefficient r included in each term is a restriction weight applied relative to each tissue. n denotes the number of normal tissues. According to the quasi-Newton's method, formula (2) is used to perform iterative calculation.                               ∇                      F            ⁡                          (                              x                i                            )                                      =                ⁢                  2          [                                                                                          r                    0                                    ⁡                                      (                    AD                    )                                                  T                            ⁢                              (                                  ADx                  -                                      Ap                    1                                                  )                                      +                                                                                r                    0                                    ⁡                                      (                    BD                    )                                                  T                            ⁢                              (                                  BDx                  -                                      Bp                    2                                                  )                                      +                                                          ⁢                                            ∑                              i                =                1                            n                        ⁢                                                                                r                    i                                    ⁡                                      (                    RD                    )                                                  T                            ⁢                              (                                  RDx                  -                  Ru                                )                                              +                                    ∑                              i                =                1                            n                        ⁢                                                                                r                    i                                    ⁡                                      (                    SD                    )                                                  T                            ⁢                              (                                  SDx                  -                  Sc                                )                                                    ]                                                      ∇            2                    ⁢                      F            ⁡                          (              x              )                                      =                ⁢                  2          [                                                                                          r                    0                                    ⁡                                      (                    AD                    )                                                  T                            ⁢              AD                        +                                                                                r                    0                                    ⁡                                      (                    BD                    )                                                  T                            ⁢              BD                        +                                                          ⁢                                            ∑                              i                =                1                            n                        ⁢                                                                                r                    i                                    ⁡                                      (                    RD                    )                                                  T                            ⁢              RD                                +                                    ∑                              i                =                1                            n                        ⁢                                                                                r                    i                                    ⁡                                      (                    SD                    )                                                  T                            ⁢              SD                                      ]            An element of a beam weight vector x giving a negative value is replaced with 0 at every time of iteration, because a beam weight must be 0 or more.
In the conventional control apparatus for controlling the radiotherapy irradiation system, the calculation time required for calculation performed under newly set restrictions is nearly equivalent to the calculation time required for calculation performed under the previous restrictions. Consequently, it takes much time to repeat calculation for different restrictions or prescriptions. Moreover, whether new restrictions are set depends on an operator.